1. Field of the Invention
The current invention relates to the field of signal equalization, particularly to enabling improved high-speed adaptive equalization.
2. Description of Related Art
Increased demand for high-speed communications services has required that economical and efficient new devices and techniques be developed to support performance increases. For example, as transmission rates climb to the 10-40 Gb/s range and beyond in modern optical networks, signal processing and conditioning techniques must be applied to filter out noise and reduce interference such as inter-symbol interference (ISI). Typical optical networks are plagued by noise and bandwidth limitations such as polarization mode dispersion and limited component bandwidth. Furthermore, the ISI can be time varying due to a variety of causes such as physical vibration, mechanical stresses and temperature fluctuations. Typically, optical receivers may use devices such as equalizers to improve the overall performance of such systems and minimize the error rate. However, the implementation of such devices has proven to be challenging and costly.
Equalizers based on transversal filters have been promoted as a way of removing noise and inter-symbol interference in some systems. For example, FIG. 1 (prior art) illustrates an example of a proposed transversal filter based equalizer 10 controlled by a microprocessor 50. In this example, the coefficients for the transversal filter may be set by the adaptation logic module, a microprocessor 50, based on analysis of eye monitor 30 data. However, this design requires the use of a clock 40 for the purpose of synchronizing data sampling. This type of design may fail in cases of severe distortion such as inter-symbol interference. For example, FIGS. 2a and b illustrate examples of eye patterns. For example, a typical eye monitor may sample in or near the “center” 60 of an eye pattern 70. However, systems experiencing severe interference may exhibit a “closed” eye pattern, 80. Typical eye monitors may fail in this situation.
Accordingly, it is desirable to have some method and device for high-speed adaptive equalization that may operate effectively even for systems experiencing severe distortion such as inter-symbol interference.